netdev - Re: [ofa-general] Re: dst_ifdown breaks infiniband?

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Date:	Mon, 19 Mar 2007 00:42:34 +0200
From:	"Michael S. Tsirkin" <mst@....mellanox.co.il>
To:	"Michael S. Tsirkin" <mst@....mellanox.co.il>
Cc:	"Eric W. Biederman" <ebiederman@...i.com>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	netdev@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	general@...ts.openfabrics.org
Subject: Re: [ofa-general] Re: dst_ifdown breaks infiniband?

> Quoting Michael S. Tsirkin <mst@....mellanox.co.il>:
> Subject: Re: [ofa-general] Re: dst_ifdown breaks infiniband?
> 
> > Quoting Eric W. Biederman <ebiederman@...i.com>:
> > Subject: Re: [ofa-general] Re: dst_ifdown breaks infiniband?
> > 
> > "Michael S. Tsirkin" <mst@....mellanox.co.il> writes:
> > 
> > >> > Why is neighbour->dev changed here?
> > >> 
> > >> It holds reference to device and prevents its destruction.
> > >> If dst is held somewhere, we cannot destroy the device and deadlock
> > >> while unregister.
> > >
> > > BTW, can this ever happen for the loopback device itself?
> > > Is it ever unregistered?
> > 
> > Well I don't think the loopback device is currently but as soon
> > as we get network namespace support we will have multiple loopback
> > devices and they will get unregistered when we remove the network
> > namespace.
> 
> Hmm. Then the code moving dst->dev to point to the loopback
> device will have to be fixed too. I'll post a patch a bit later.

Does this look sane (untested)?

Signed-off-by: Michael S. Tsirkin <mst@....mellanox.co.il>


diff --git a/net/core/dst.c b/net/core/dst.c
index 764bccb..8283158 100644
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -235,6 +236,8 @@ again:
 static inline void dst_ifdown(struct dst_entry *dst, struct net_device *dev,
 			      int unregister)
 {
+	struct neighbour *neigh;
+
 	if (dst->ops->ifdown)
 		dst->ops->ifdown(dst, dev, unregister);
 
@@ -245,14 +248,13 @@ static inline void dst_ifdown(struct dst_entry *dst, struct net_device *dev,
 		dst->input = dst_discard_in;
 		dst->output = dst_discard_out;
 	} else {
-		dst->dev = &loopback_dev;
-		dev_hold(&loopback_dev);
-		dev_put(dev);
-		if (dst->neighbour && dst->neighbour->dev == dev) {
-			dst->neighbour->dev = &loopback_dev;
-			dev_put(dev);
-			dev_hold(&loopback_dev);
+		neigh = dst->neighbour;
+		if (neigh && neigh->dev == dev) {
+			dst->neighbour = NULL;
+			neigh_release(neigh);
 		}
+		dst->dev = NULL;
+		dev_put(dev);
 	}
 }
 

-- 
MST
-
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